The invention relates generally to the field of electric power generation and more specifically to the field of wind generated electric power.
The world wind electric potential has not been tapped before because wind turbine-technology was not able to utilize this resource. However, during the past decade, increased knowledge of wind turbine behavior has led to more cost-effective wind turbines that are more efficient in producing electricity. The price of the electricity produced from wind by these advanced turbines is estimated to be competitive with conventional sources of power, including fossil fuels. Because of the increasing competitiveness of wind energy, wind resource assessment will become essential in incorporating wind energy into the nation""s energy mix.
Detailed wind resource assessments have been proposed or are being considered as part of a plan to increase the use of wind energy in Europe, Asia, Latin America, and other regions. The decreasing cost of wind power and the growing interest in renewable energy sources should ensure that wind power will become a viable energy source in the United States and worldwide.
The United States has tremendous wind energy resources. Although California gave birth to the modern U.S. wind industry, 16 states have greater wind potential. Installed wind energy generating capacity totaled 2,550 MW in 2000 and generated about 5.5 billion kWh of electricityxe2x80x94less than 1% of U.S. electricity generation. By contrast, the total amount of electricity that could potentially be generated from wind in the United States has been estimated at 10,777 billion kWh annuallyxe2x80x94three times the electricity generated in the U.S. today.
The American wind energy industry is poised for rapid growth in 2001. At least 40 projects in 20 states are proposed to come online, boosting U.S. wind energy capacity by 2,000 MW to 4,500 MW. These new wind farms demonstrate how wind energy can help meet the growing need for affordable, reliable power in the West and other regions of the United States.
By adjusting the connections between stator coils between series and parallel connection based on present operating conditions, a generator can operate effectively at a wide range of shaft speeds. Boost circuitry can further enhance the performance of the generator at low shaft speeds.
A segmented arc generator is adapted to convert mechanical power such as wind or water power into electrical power. A rotor is provided having a plurality of salient poles disposed about a periphery of a rotor ring that features a support structure for maintaining the radial position of the salient poles when the rotor rotates as a result of being driven by a prime mover. A stator is provided having a stator ring disposed radially about and in close proximity to the rotor ring. The stator ring includes a plurality of stator coils wound on a ferromagnetic structure and having permanent magnets imbedded within the structure. Relative motion between a rotor pole and a corresponding stator coil induces a coil voltage across that coil. A phase controlled converter in electrical communication with the stator coils rectifies the output voltage of the coil by passing a variable portion of the coil voltage to approximate a D.C. voltage. A voltage controller monitors the D.C. voltage and controls the phase controlled converter to pass a portion of the coil voltage that maintains a relatively constant D.C. voltage. A pulse width modulated inverter is in electrical communication with the phase controlled converter for converting the D.C. voltage output of the phase controlled converter to an A.C. voltage of controlled amplitude and phase relationship determined with respect to a voltage waveform present on a connected utility grid. A switching matrix selectively places the coils in series or parallel or a combination of series and parallel connections with respect to one another in response to control signals that are based on present operating conditions of the generator.
According to a preferred embodiment, a boost converter circuit provides and maintains a minimum D.C. voltage to the pulse width modulated inverter when the voltage induced in the coils falls below a threshold value. The boost converter circuit includes a storage device that is activated by a switch to selectively store and discharge energy to the pulse width modulated inverter. According to one embodiment, the boost converter circuit features an inductor connected in series with the output of the phase controlled converter, a transistor connected by its collector to the inductor and by its base to ground, and a diode connected between the collector and the input of the pulse width modulated inverter. The voltage controller provides gate voltage pulses to the transistor of controlled duration when the D.C. voltage falls below a predetermined level to periodically charge and discharge the inductor to supply a D.C. voltage of increased magnitude to the pulse width modulated inverter.
In one embodiment, the switching matrix removes stator coils from operation based on generator operating conditions. The rotor support structure can include integrally formed fan blades that rotate when acted upon by the wind to rotate the rotor within the stator or the prime mover may alternatively be a fan driven shaft. A plurality of rotor and stator pairs can be used together to increase output power.